Affiliate Marketing Secrets

A year ago, I sold a car to someone who never returned my license plates. Then a few months later USAA sent me a letter saying that I was at fault for a car accident. I was scared, and realized that this woman had gotten a hold of my license plates and got in a car crash and the cops didn’t run all the info all the way through.
I had filed a report about the stolen license plates but I never got a chance to get the actual police report and they had a hard time finding it without the number they wrote on a card for me. Well I got the registration for the car the license plate belonged to and sent it to USAA to finish it out and they said they were good and that the woman who actually was in the accident wanted to accept full financial responsibility.
Recently the financial department from an insurance company that was affiliated with USAA has been coming after me since the woman hasn’t payed recently. Can they still do that?
The dept. of safety in my state sent a letter to me saying:
” We have recieved a release submitted for the crash that occurred on SEP 1, 2011.”
Can I get out of this and doesn’t the letter from the dept. of safety mean that I am no longer responsible?